Drain pumps and similar high voltage generating circuits are utilized to provide high voltage and/or high current for semiconductor operation. For example, in semiconductor memory devices, drain pumps are used to provide high voltage and high current for programming memory cells. Typically, drain pumps include large capacitors. To conserve power, the drain pumps are turned on and off frequently depending on the output voltage thereof. Because of the capacitors, each time the drain pumps are turned on or turned off, they create noise on the power buses (e.g., Vcc and Vss). In addition, while the drain pumps are ramping up to a steady state voltage level after being turned on, they also create noise on the power buses. This noise increases as the size of the drain pump increases. Some circuits, particularly voltage reference circuits in semiconductor memory devices, require a very quiet power bus and the noise from the drain pumps is generally unacceptable.
Accordingly, it is desirable to provide a method and apparatus for drain pump operation which conserves power while reducing the noise generated by conventional power conservation schemes. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.